Abstract We present accurate maps of the CO J=2-1 and 1-0
lines made with the Plateau de Bure interferometer of the gas disk
around the central star(s) of the Red Rectangle, a well known
protoplanetary nebula. We confirm that the molecular gas in this source
forms a disk perpendicular to the conspicuous axis of symmetry of the
optical nebula and that this disk is in rotation.
We present detailed modeling of the CO emission and extensive
discussion of the accuracy of the values fitted for the different
parameters. The outer radius of the disk is ~
(
) cm, as a function of the assumed distance D, which is thought to vary between 380 and 710 pc.
The rotation is found to be
Keplerian, at least in the inner disk. From this velocity field, we
derive a central mass between 0.9 , for a distance of 380 pc, and 1.7 , for 710 pc.
Previous studies of the nature of the stellar component favor the
highest values.
In the outer disk, we deduce the presence of a slow expansion velocity
(~0.8 km s-1), superimposed on rotation. We find gas
temperatures decreasing from ~400 to 30 K across the disk and
densities cm-3.